Modern hard disc drives comprise a mechanical housing which encloses one or more rigid discs that are rotated at a constant high speed. Data are stored on the discs in a plurality of concentric circular tracks by an array of transducers ("head") mounted to a radial actuator for movement of the heads relative to the discs.
The heads are mounted via flexures at the end of a plurality of arms that project radially outward from an actuator body. The actuator body pivots about a pivot shaft, such as a vertical post which extends upwardly from the housing. The post is parallel with the axis of rotation of the discs so that the heads move in a plane parallel with the surface of the discs.
Typically, such radial actuators employ a voice coil motor to position the heads with respect to the disc surfaces. The voice coil motor includes a magnetic circuit mounted to the disc drive housing and a coil mounted on the side of the actuator body opposite the head arms so as to be immersed in the magnetic field of the magnetic circuit. When controlled current is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the post and the heads move across the disc surfaces.
In the manufacturing of a disc drive, it is important that the actuator assembly be placed in the proper location, centered on all three axes, longitudinal, latitudinal, and translational (x, y, and z) with respect to the discs. Typically, the actuator assembly has a large bored recess which accommodates a cartridge bearing assembly with a pair of ball bearing assemblies to accommodate rotation of the actuator assembly about the z-axis. The cartridge bearing assembly includes an inner bored recess to allow the actuator assembly to fit over the pivot post. The diameters of the large bored recess and the inner recess are maintained within predetermined, close tolerance ranges.
A tolerance ring can be advantageously used to compensate for variances of the part manufacturing tolerances and thus retain the proper positioning of the actuator assembly in all three axes. Typically, prior art tolerance rings consist of a corrugated sheet of metal formed into an open cylindrical shape. The tolerance ring is then provisioned around the post and stationarily held in position by an anchoring groove in the pivot post. In most applications, the tolerance ring serves only as a manufacturing aid and provides no additional function after completed manufacture. Exemplary prior art tolerance ring configurations are disclosed in U.S. Pat. No. 5,315,465 issued to Blanks, U.S. Pat. No. 4,286,894 issued to Rongley, and U.S. Pat. No. 3,838,928 issued to Blaurock et al.
Although widely used, most prior art tolerance rings fail to exhibit adequate hoop strength. Hoop strength is a measure of the grasping force that a tolerance ring is capable of exerting when engaged with the pivot post. Significantly, inadequate hoop strength may cause an impermissible degree of movement between the tolerance ring and the pivot post. Consequent placement of the actuator assembly over an improperly positioned tolerance ring may cause the tolerance ring to foul or be forced out of the anchoring groove.
Additionally, a tolerance ring with insufficient hoop strength is susceptible to deformation during shipping and handling. Frequently as a result of mishandling the tolerance ring experiences a helical deformation in which the tolerance ring "twists" about a central axis, thereby rendering the tolerance ring useless for subsequent manufacturing purposes. The likelihood of deformation during shipping and handling reduces the efficiency of the manufacturing process by necessitating the inspection of the parts before introduction into automated assembly.
With an increasing demand for improved consistency in the installation of actuator assemblies, there remains a continuing need for the development of a tolerance ring which is resistant to deformation and which exhibits increased hoop strength. It is to such improvements that the present invention is directed.